Scientists believe the expanding early Universe produced waves of sound that echoed through the dense plasma and hydrogen that filled it at the time. Obviously, these sound waves are no longer audible, but using information on cosmic background radiation collected by NASA probes it is possible to simulate the sound.

This colossal sound wave shaped cosmic background radiation so that some areas remain hotter or colder. In 2003, University of Washington physicist John Cramer mapped those hot and cold variations to produce a sound file; a 100-second "recording" of the Big Bang.

Cramer wrote a science-based column for Analog Science Fiction & Fact magazine in 2001, describing the likely sound of the Big Bang based on cosmic microwave background radiation observations taken from balloon experiments and satellites. A few years later, the mother of an 11-year-old boy working on a science project read the article and asked if the sound of the Big Bang had actually been recorded anywhere. It hadn't been yet, but this had Cramer thinking maybe it should be.

Using data from NASA's Wilkinson Microwave Anisotropy Probe (WMAP) on cosmic background radiation temperature fluctuations in the early Universe, Cramer fed the wavelength changes into a computer program called Mathematica to convert them to sound. The resulting 100-second recording represented the sound from approximately 380,000 years after the Big Bang until about 760,000 years after.

“The original sound waves were not temperature variations, though, but were real sound waves propagating around the universe,” he said.

The 2003 data lacked high frequency structure, Cramer noted in a recent statement. This year, he used new data to re-master his recording.

The Verge reports that the data for the new recording came from the European Space Agency's (ESA) Planck satellite mission. Planck has detectors so sensitive that they can distinguish temperature variations of only a few millionths of a degree in the cosmic microwave background. In March of this year, the Planck mission released a new and more precise map of cosmic microwaves that allowed Cramer to create the new sound file based on temperature fluctuations mapped onto an ESA graph.

Cramer manually recorded each of the data points, and then created a monaural sound wave following the frequency spectrum. The sound wave was adjusted to account for how the sound would have changed as the Universe stretched, "becoming more of a 'bass instrument.'" As the wavelengths are stretched farther, the sound becomes lower and at first louder, eventually fading out. In fact, the sound was so "bass" that Cramer had to boost the frequency 100 septillion times to put it into the human hearing range.

Cramer has been part of a research group working on what the Universe might have been like moments after the Big Bang using collisions between heavy ions, such as gold, in the Relativistic Heavy Ion Collider at Brookhaven National Laboratory.

“It was an interesting thing to do that I wanted to share. It´s another way to look at the work these people are doing,” he concluded.